The present invention relates to a keyboard assembly for providing electrical outputs corresponding to multiple keys, to signal utilization electronic devices such as typewriters and other data processing equipment.
In such a keyboard for electronic devices, a multiplicity of keys are disposed in plural rows to provide electric signals corresponding to the keys which have been depressed on their top faces. To improve ease of operation of the keys, attempts based on human engineering or ergonomics have been made to arrange the keys such that an operating surface generally defined by the top faces of the individual keys is curved to a downwardly convex shape in cross section taken along a line perpendicular to the rows of the keys.
A keyboard, which can be manufactured at low cost, is proposed as disclosed in U.S. patent application, Ser. No. 598,920 filed Apr. 10, 1984 now U.S. Pat. No. 4,528,428, assigned to one of the assignees of the present application, and in U.S. patent application, Ser. No. 624,395 filed June 25, 1984 in the name of the present inventors. Such a keyboard has multiple key-switches each comprising a key having a finger-pressed top face, a movable electrode and at least two stationary electrodes. The keyboard includes a key holder plate of generally planar flat shape and retaining means thereof. The key holder plate supports the multiple keys in plural rows movably in a direction perpendicular to a plane of the key holder plate, and has holes through which the keys extend and integral guide portions formed around each of the holes and extending in the aforementioned direction. The key holder plate further has a deformation-facilitating portion located between each pair of adjacent rows of the plural rows of keys. The deformation-facilitating portion has a single longitudinal recess formed in parallel to the rows of keys. The retaining means holds the key holder plate such that the plate is downwardly convexed in cross section across the rows of keys mainly owing to elastic deformation of the deformation-facilitating portion, whereby a surface generally defined by the top faces of the multiple keys is downwardly convexed in the cross section.
In such a keyboard, the key holder plate is curved downwardly after assembling, whereby multiple guide portions provided in the key holder plate are directed unparallel to each other. If it is attempted to mold a key holder plate of such a shape, molds would inevitably be extremely complicated in structure to enable the removal of a molded key holder plate from the molds, and molding cycle time would also be long. However, since the key holder plate of the preceding applications is generally of a planar flat shape and multiple guide portions are directed parallel to each other before assembling, the key holder plate can be molded in simply structured molds which can be opened and closed in a direction perpendicular to the key holder plate, resulting in reduced cost of manufacture of the keyboard.
In order to facilitate elastic deformation of the key holder plate as mentioned above, it is desired to reduce the thickness of the key holder plate. In consideration of a molding process and rigidity of the key holder plate, however, it is not desired to reduce the thickness of the key holder plate. In the keyboard described in the specifications of the two preceding applications, therefore, the key holder plate is provided with recesses each formed in a deformation-facilitating portion located between two adjacent rows of keys such that these portions are curved more easily than the other portions. Each of these recesses has a long longitudinal shape formed in a direction parallel to the rows of keys, and only one recess is provided between two adjacent rows of keys of the key holder plate as viewed in a direction perpendicular to the rows of keys.